When a semiconductor wafer is cut into multiple chips by a dicing cut method, the position of the wafer is aligned by using an alignment marker (i.e., a scribe marker). Specifically, the wafer is positioned in such a manner that the alignment marker on the scriber is aligned from the surface of the wafer. Thus, the wafer is cut into multiple chips. However, as shown in FIGS. 9A to 9C, when a plurality of physical quantity sensors having a beam structure 100 as a movable portion are formed on the surface of the wafer, it is necessary to protect the beam structure 100 during the wafer dicing. Specifically, the beam structure 100 is protected by applying an adhesive tape 101 on the surface of the wafer. Then, the wafer is cut from a backside of the wafer, which is opposite to the beam structure 100. This dicing method is disclosed in Japanese Patent Application Publication No. 2000-223446. At this time, as shown in FIG. 10, a light source 102 for emitting a light having a wavelength capable of transmitting the silicon wafer is disposed on the foreside of the wafer. The light is transmitted through the wafer. Then, the light is detected by an imaging device 103. The imaging device 103 is disposed on the backside of the wafer. As shown in FIG. 11, an outline of the beam structure 100 is aligned with a dicing line so that the wafer is positioned. Specifically, the positioning of the wafer is performed by using the edge of the beam structure 100, and then, the wafer is cut along with the dicing line.
When the beam structure 100 is formed from a concavity 104 having an opening for opening to the backside of the wafer, the beam structure 100 can be projected by the light transmitting through the silicon wafer. Thus, the image of the beam structure 100 is clear and obvious so that the accuracy of positioning of the wafer is high even when the backside of the wafer is rough.
However, as shown in FIG. 12, when the wafer includes a support substrate 110, which is disposed under the beam structure 100, the light transmits the support substrate 110. Therefore, the light may be scattered at the backside of the wafer. Thus, it is difficult to align the wafer. This is because it is difficult to observe the outline of the beam structure 100 clearly and accurately. Thus, the accuracy of the positioning method of the wafer is reduced.